Biodegradable polyester is a kind of macromolecule material using biological resources as raw materials. With respect to a petroleum-based polymer using petrochemical resources as raw materials, the biodegradable polyester can be degraded during a process of biological or biochemical effect or in a biological environment, being a very active degradable material in the present biodegradable plastic research and one of the best degradable materials in market application.
At present, biodegradable polyester film takes one of the most important application fields of biodegradable polyester, mainly including grocery bag, garbage bag, shopping bag, mulching film and the like. During blow molding process of the biodegradable polyester in preparing films, it frequently appears that the film is not lubricating enough to adhere to a roll or is too lubricating to roll up. Thus it results in poor bubble stability and large range of film thickness during film blowing which severely affect a continuity of film blowing. In CN 101622311A, by adding 0.05-5 wt % of biodiesel into a biodegradable polyester mixture, a viscosity of the polyester mixture is decreased, to some extent leading to less adherence of film to the roll, which guarantees the continuity of film blowing. However, a decrease of the viscosity of the polyester mixture indicates that an addition of biodiesel damages performances of the polyester to some extent, resulting in an increased melting index and a decreased viscosity of the polyester mixture.
In addition, owing to effects of microorganism, illumination, radiation, atmosphere and contacted physical environment, a molding product prepared with the biodegradable polyester is relatively easy to age and degrade during storage and use, which hugely influences service performance of the product. A conventional method that solves the aging and the degradation of macromolecule material includes adding an antioxidant, a UV absorbent, a HALS stabilizer and the like into the material. For example, patent WO 2009/071475 discloses a mulching film of polyethylene which contains hydroxyphenyltriazines as the stabilizer. CN 103687902 introduces the UV absorbent and the HALS stabilizer, or a light stabilizer combining both, for providing the mulching film with UV stability. Although the above stabilizers can provide certain stabilization, they are definitely not satisfactory for a transparent mulching film, especially for that with a relatively thin wall thickness.
Besides, under a condition that the molding product prepared with the biodegradable polyester composition is digested with 95% ethanol, there will be a precipitate separating out of a surface of a film or a part, which thus influences a surface appearance property of the film or the part.
The present invention surprisingly finds by research that by adding a trace amount of a cyclic ester compound and cyclopentanone into the biodegradable polyester composition, an anti-oxidative property of the biodegradable polyester composition can be greatly enhanced, and meanwhile it guarantees that the biodegradable polyester composition has an excellent surface appearance property and enables the biodegradable polyester composition to have obviously improved film blowing properties. When a velocity of film blowing is relatively high, it presents good bubble stability as well as relatively small range of film thickness and guarantees the continuity of film blowing production.